Re: Interacting with a input kernel driver from user space

[Nuno Santos <nsantos@edigma.com>]

     Why? I thought this thing is an input device? Why does an 
application have to modify a running device? Is this modification local 
to the application<->device interface or does it also affect all other 
running applications that use this device? If it is a configuration 
value to put the device into a different state or similar, then you can 
use a sysfs attribute. The user can change this with "echo <value> 
 >/sys/class/input/inputX/<attribute>"

I'm already with working examples of ATTRIB in my driver project. The 
thing is that I have random kernel panics when I try to read from the 
attribute. This is my attribute code:

static ssize_t usbtouchscreen_get_state(struct device *dev, struct 
device_attribute *attr, char *buf)
{
     int count=0;
     struct usbtouch_usb *usbtouch = dev_get_drvdata(dev);
     struct dpx_priv *priv = usbtouch->priv;

     printk(KERN_INFO "state length: %d",sizeof(DPX_DEVICE_STATE)); // 
size = 43196 bytes

     memcpy(buf,(void*)&priv->context->State,sizeof(DPX_DEVICE_STATE));

     return sizeof(DPX_DEVICE_STATE);
}

static DEVICE_ATTR(state, 0777, usbtouchscreen_get_state, NULL);

Should I make anykind of protection while doing this operation? I have 
read in some answer from you guys, that I should create an attribute for 
every field of the structure I want to bring to userspace, but that will 
make me have tenths of attributes. The problem for me are not the number 
of attributes, but the changes I will need to have in my control panel 
to support that architecture. One attribute with the content of State 
variable would be perfect.

Any ideas?

Thanks,

Nuno